1. Field of the Invention
The present invention relates to a color image forming apparatus that uses an electrophotographic process or the like.
2. Description of the Related Art
An image forming apparatus having a configuration to use an intermediate transfer member is known as an electrophotographic type image forming apparatus. In this image forming apparatus, as a primary transfer step, a toner image is formed on a photosensitive drum (image bearing member: first image bearing member) of each image forming station, such as yellow (Y), magenta (M), cyan (C) and black (Bk). Then a toner image with a plurality of superimposed colors is formed by sequentially transferring the toner image on each photosensitive drum to the surface of an intermediate transfer belt (intermediate transfer member). Then as a secondary transfer step, the toner image with a plurality of colors formed on the surface of the intermediate transfer belt is transferred in batch to the surface of a recording material, such as paper. The toner image with the plurality of colors transferred in batch to the recording material is permanently fixed to the recording material by a fixing unit, and is formed on the recording material as a color image.
In some cases the image forming apparatus performs various image forming apparatus adjustment processing during continuous image formation or after image formation ends, as a separate step from an image forming step. For example, a turn-up prevention control for a cleaning blade, which is used for cleaning the toner off the image bearing member inside the cartridge, will be described as an image forming apparatus adjustment processing. In an image forming apparatus that includes a cleaning blade, if toner on the cleaning blade nip runs out and the friction force of the blade becomes excessive, faulty cleaning may occur and eventually a blade turn-up may occur. To prevent this faulty cleaning and blade turn-up, toner is periodically supplied to the cleaning blade nip, so as to lubricate the blade (hereafter called “toner ejection processing”).
Whether this control is executed or not is normally determined by a number of pages, printing rate or the like of the images to be formed. If the toner ejection processing execution conditions are satisfied during continuous image formation or after image formation ends, the image forming apparatus interrupts the image forming processing if it is during the image formation, and forcibly forms an electrostatic latent image on the photosensitive drum, and this image is visualized as a toner image. In the toner image formed here, a potential of the primary transfer portion has reversed polarity of the polarity used for primary transfer; therefore, this toner image is not transferred to the intermediate transfer belt, but is supplied to the cleaning blade unit.
In the above mentioned image forming apparatus adjustment processing, the primary transfer portion must be controlled independently from the secondary transfer portion, and in the case of a conventional configuration where the primary transfer portion and the secondary transfer portion have a high voltage power supply, respectively, predetermined potential polarity can be outputted by independently controlling voltage and current for the primary transfer portion and the secondary transfer portion, respectively. In other words, regardless of the transfer state of the secondary transfer portion, the primary transfer portion can output a predetermined potential polarity independently, and perform processing. However, Japanese Patent Application Laid-Open No. 2012-137733 proposes a configuration to perform both the primary transfer and the secondary transfer using current supplied from the secondary t ransfer portion to the intermediate transfer belt.
It is difficult, however, to independently control the potential polarity of the primary transfer portion and the secondary transfer portion since the potential polarity of the primary transfer portion is controlled by voltage applied to the secondary transfer member. Depending on the switching timing of the potential polarity, toner of the secondary transfer portion may adhere to a recording material passing through the secondary transfer portion.